As rectangular waveguides met with increased usage during the early 1960s, a number of problems developed. Typical towers varied in height from 50 to 2,000 feet, and they were and still are constructed of steel members because of the strength requirements. On the other hand, the typical waveguide was and is made of aluminum which expands and contracts twice as much as steel when the surrounding atmospheric temperature changes. Accordingly, the waveguide will undergo severe stresses, and consequently severe deformations, if constrained in the vertical or axial direction as the seasons run through their normal cycle. The waveguide also undergoes substantial stresses due to wind loads and, consequently, would undergo severe deformation or distortion if not supported judiciously. Such deformations have a tremendously deleterious effect on the waveguide's ability to transmit energy efficiently, that is, without ghosting and other abnormalities in the transmitted signal.
It has been known heretofore to suspend waveguides from transmission towers by means of helically coiled extension springs and a constant force mechanism to compensate for the differential expansion rates between the tower and the waveguide. However, such systems have a number of disadvantages, among which are the large hanger size required, thereby necessitating a substantial distance from the waveguide center line to the hanger mounting surface on the tower, which results in a lack of rigidity. Also, excessive clearance area is required in order to accommodate the spring mechanism. Other disadvantages reside in the criticallity of the initial setting of the springs to conform correctly to the temperature at time of installation, allowing for proper extension and contraction during future temperature changes.
Another waveguide suspension system that has been known makes use of conventional helical springs on the hangers to support the waveguide. This type of suspension also has disadvantages, such as large variations of spring force encountered with large temperature changes. Also, there is a requirement for excessive length in the spring in respect of its working area.
A spring hanger system specifically for a UHF circular waveguide is disclosed in U.S. Pat. No. 3,654,612, and this system overcomes many of the drawbacks already noted. However, the invention described in that patent is directed to the mounting of a large-sized UHF circular waveguide and is not suitable for supporting a rectangular waveguide.